1. Field
The present disclosure relates to an electronic apparatus that has the function of projecting images and, in particular, to adjustment of a focal length of a projected image.
2. Description of the Related Art
A method for projecting images in the direction of a driver's line of sight has been known as a display system that reduces motion of the driver's line of sight while driving the vehicle. This kind of display system is also called head up display (hereinafter, abbreviated as HUD). The HUD is a system that forms an image from an image projecting device placed in a vehicle on a windshield or a screen on the windshield and thus creates a virtual image that enables an object to seem to exist in a real space through the screen. The driver can reduce the number of times that they look at a display device or the like inside the vehicle by viewing the virtual image through the screen.
While the HUD is becoming widespread, meters (for example, speed meter, gear position indicator, fuel gauge, and similar instruments) attached to an instrument panel in front of the driver's seat are being displayed in an electronic digital form. Those meters may be displayed by, for example, a single horizontally long liquid crystal display unit. Hereinafter, a unit that electronically displays the meters on the instrument panel is referred to as a cluster display unit. When the HUD and the cluster display unit are both placed in the vehicle, the driver can switch between the HUD and the cluster display unit depending on the state, such as during movement or at a standstill. Japanese Unexamined Patent Application Publication No. 2014-91466 discloses a vehicle information display device including both a HUD and a cluster display unit. In that vehicle information display device, a dedicated HUD display area is provided at an upper portion of the cluster display unit to minimize motion of a driver's line of sight and changes in a focal point.
When an image displayed by the cluster display unit and an image displayed by the HUD cooperate with each other, the driver must look at each indication by the cluster display unit and that by the HUD. In that case, because the cluster display unit is in a position relatively near to the driver's seat, and the image displayed by the HUD is typically a virtual image in the distance on the windshield as seen from the driver's seat, the focal lengths of both images are not the same in most cases. Accordingly, if the driver tries to move the line of sight between both images, they must readjust the focus for each movement, and this leads to reduced visibility. There is a method of making both focal lengths uniform by providing a dedicated HUD display area at an upper portion of a cluster display unit, as illustrated in the above-mentioned patent literature. In that case, however, it is difficult to achieve depth in images displayed by the HUD.